linux-kernel - Re: [PATCH 1/1] mtd: mtdoops: fix for a potential memory leak in mtdoops_notify

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Message-ID: <CAGq6Fke=DYbK=KO6RdTD2at9NPMKcmxzOQ2TL6fBfM2UgSOfRQ@mail.gmail.com>
Date:	Tue, 13 Aug 2013 09:41:28 +0530
From:	Nilanjan Roychowdhury <nilanjan.roychowdhury@...il.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] mtd: mtdoops: fix for a potential memory leak in mtdoops_notify_remove

On Mon, Aug 12, 2013 at 10:56 PM, Ezequiel Garcia
<ezequiel.garcia@...e-electrons.com> wrote:
>
> On Sun, Aug 11, 2013 at 01:11:48PM -0700, Nilanjan Roychowdhury wrote:
> > we are allocating cxt->oops_page_used using vmalloc in mtdoops_notify_add for
> > every mtd_info addition but not freeing it in mtdoops_notify_remove
> >
> > Signed-off-by: Nilanjan Roychowdhury <nilanjan.roychowdhury@...il.com>
> > ---
> >  drivers/mtd/mtdoops.c |    1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
> > index 97bb8f6..02f49aa 100644
> > --- a/drivers/mtd/mtdoops.c
> > +++ b/drivers/mtd/mtdoops.c
> > @@ -386,6 +386,7 @@ static void mtdoops_notify_remove(struct mtd_info *mtd)
> >       cxt->mtd = NULL;
> >       flush_work(&cxt->work_erase);
> >       flush_work(&cxt->work_write);
> > +     vfree(cxt->oops_page_used);
> >  }
> >
> > --
> > 1.7.9.5
> >
>
> Have you tested this patch doing an unregister/module remove cycle?
>
> I'm not entirely sure, but I *think* you must also remove the
> vfree(cxt->oops_page_used); at mtdoops_exit(). Otherwise,
> you might call vfree() twice, the second time on a garbage pointer.
>
> The reason for this is that the unregister_mtd_user(&mtdoops_notifier);
> call in mtdoops_exit() will call the .remove callback (causing the first
> vfree() with this patch) and then call vfree() for the second time, explicitly.
> --
> Ezequiel García, Free Electrons
> Embedded Linux, Kernel and Android Engineering
> http://free-electrons.com
i did not do a module remove. I agree with your observation. I will
resubmit the patch.
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